A nickel hydroxide is used for a nickel electrode of an alkaline secondary battery. Nickel hydroxides include an a type and a β type, and the nickel hydroxide for an alkaline secondary battery widely used at present is β-nickel hydroxide. An oxidation-reduction reaction at the time of charge-discharge of an active material of the nickel electrode is a “one-electron reaction” in which the oxidation number of nickel varies from +2 to +3.
On the other hand, in recent years, an increase in capacity is required of the nickel electrode, and it is proposed to use α-nickel hydroxide as an active material. While the reaction of the β-nickel hydroxide is a one-electron reaction, a multi-electron reaction takes place in the α-nickel hydroxide, and therefore the α-nickel hydroxide enables to outstandingly improve the capacity per nickel weight.
However, when the α-nickel hydroxide is used for the electrode, there is a disadvantage that initial activation of the battery is hardly achieved. In general, in the alkaline secondary battery using a nickel hydroxide electrode, activation of the nickel hydroxide is achieved to a degree suitable for charge-discharge by repeating charge-discharge cycles several times to about ten times before completion of the battery. When the activation of the nickel hydroxide is hard, there is a possibility that not only the number of activation steps in the production process of the alkaline secondary battery is increased, but also a damage or capacity deterioration of the battery occurs.
In order to solve these problems, an effort to constitute a nickel electrode by adding a hydroxide of erbium or thulium, or an oxyhydroxide to the α-nickel hydroxide has been made (JP-A-2003-249214). However, in such a case, an additive not involved in charge-discharge is used in the electrode, and the ratio of the active material in the electrode decreases, and therefore, the substantial discharge capacity is reduced.